How are aluminum extrusion made?

Aluminum extrusions are principally produced from aluminum billet. The billet is softened by being heated to the necessary temperature before extrusion. Under the direct extrusion process, the heated billet is then placed into a hydraulic extrusion press where a ram pushes a dummy block to force the softened metal through a precision opening, or die, to produce the desired shape. As pressure is applied against the die, the billet becomes shorter and wider until its expansion is restricted by full contact with the container walls. As the pressure increases, the softened metal begins to squeeze out through the shaped orifice of the die and emerges as a fully formed profile. Under indirect extrusion, the die is contained within the hollow ram, which moves into the stationary billet forcing the metal to flow into the ram, acquiring the shape of the die as it proceeds. In either process the aluminum exiting the die acquires the same cross-sectional shape as the die. After emerging from the die, the extrusion is cooled, either naturally or through air or water quenching. The following steps are usually performed after cooling.

? Stretching.

After the extruded part has been cooled, a stretcher and/or straightener may be used to straighten the extrusion and correct any twisting that may have occurred during and after the extrusion process?

?Cutting.

The profile is typically cut in order to reduce it to the specified commercial length.?

Aging.

Certain extrusion alloys reach optimal strength through the process of aging, or, agehardening. The aging process ensures the uniform precipitation of fine particles through the metal, producing an alloy with maximum strength, hardness, and elasticity. Natural aging occurs at room temperature and artificial aging occurs through controlled heating in an aging oven. Non-heat-treatable aluminum alloys, including 3000 series alloys utilizing manganese, are subject to natural aging. Artificial aging, also known as precipitation heat-treating, occurs through controlled heating in an aging oven

Mechanical finishes.

These processes include buffing and burnishing to achieve a smooth finish and blasting or scoring to achieve a rough finish. Mechanical finishes are accomplished using specific types of equipment. Other mechanical finishes include sanding,polishing, and tumbling.?

Anodizing.

This process involves the use of electrolysis to encourage oxygen ions to combine with aluminum to form a hard aluminum oxide film or seal, thus enhancing the durability and beauty of the profile. Pretreatment steps to the anodizing process may include alkaline cleaning to remove organic contaminants and acid cleaning to remove inorganic contaminants. The extrusion profile is immersed in a tank containing an acid-based electrolyte solution. Electric current is passed through the solution while the temperature is carefully controlled. The electric current causes oxygen ions to be released from the electrolyte solution and to be drawn to the surface of the aluminum profile, which serves as an anode.

Bright Dipping.

This is a type of anodizing process. The aluminum extrusion is first polished to remove fine scratches and then submerged typically in a phosphoric acid and nitric acid bath and heated to an elevated temperature. It is then anodized to protect the surface finish and to apply color to the profile.

Etching.

Under chemical etching the aluminum profile is passed through a caustic solution bath, rinsed, and then immersed in another bath to dissolve unwanted alloy surface impurities.

Painting.

Both specialty liquid paints and powder coatings may be applied to the aluminum profile. Thermoplastic or thermoset polymer powder coatings are applied using an electrostatic gun to impart a positive electric charge to the powder. The powder is accelerated toward and adheres to the negatively charged aluminum profile. After the powder is applied, the profile is baked in an oven where the powder particles are melted to a liquid state which then fuses with the profile to form a homogeneous surface finish. The surface is then cooled to form a hard coating.

Fabrication.

Fabrication processes generally include machine tooling operations such ascutting to precision lengths, machining, drilling, hole-punching, notching, bending, and stretching to prepare the profile for its final use.?

Refer: www.usitc.gov